Products > Test Equipment

AN8008 US $19, 9999count, 1uV, 0.01uA, 0.01Ohm, 1pF resolution meter

<< < (138/172) > >>

jackenhack:

--- Quote from: JohnPen on October 13, 2017, 04:08:07 pm ---In a fit of enthusiasm I decided to add extra decoupling to my AN8008 3v rail.  Thanks to Jackenhack I decided to progressively add a 1000pfd, a 0.01ufd, a 0.1ufd and finally a 4.7ufd. With each addition I observed the impact on the 3v rail with a scope.  The first 2 capacitors had very little effect but adding the 0.1ufd definitely improved things. Finally adding the 4.7ufd really improved the stability of readings and startup on the volts range was an almost immediate to zero (This was with no probe leads attached as pickup in the leads has an impact on the readings).   I left all the additional capacitors in place as well as the untouched original 100ufd  and the meter is now much more stable than before.  A very  worthwhile modifcation.

--- End quote ---

Great to hear. All props goes to floobydust who put me on the right track.
The 0.1 µF capacitor definitely improved the high frequency noise, but to knock down the 1.1 KHz spike, I had to replace the 100 µF cap with a 1000 µF one. I guess the voltage reference have more problems with the higher frequency noise than the big ones at 1.1 KHz. Anyway, the voltage rail looks like when a CPU is doing micro-sleeps to save power, something is definitely injecting noise to the 3 V rail.

GreyWoolfe:

--- Quote from: stj on October 13, 2017, 07:57:27 am ---you could use a broken harddrive.
they usually have 10 or 22uf ceramics on them.

--- End quote ---

The couple of hard drives I have floating around here are still good and are company property.  The only bad ones I had were also company property and I had to ship them to our main office for destruction.  The caps are cheap enough and I have other stuff i need for another couple of projects, so I will have an order that's worth it for the shipping.

stj:
a quick cross-link to a discovery of interest in the 8001/2 thread.
https://www.eevblog.com/forum/testgear/aneng-an8001-6000-count-true-rms-multimeter/msg1322321/#msg1322321

exe:

--- Quote from: JohnPen on October 13, 2017, 04:08:07 pm ---progressively add a 1000pfd, a 0.01ufd, a 0.1ufd and finally a 4.7ufd.

--- End quote ---

I think it's better not to mix more than two types of caps on the rail as they resonate. Detailed explanation: .

I ended up installing one 1uF polyester cap in addition what was already installed in my DMM. HF-noise mostly gone, still, there are dips 6.3mV p-p. I don't have a good electrolytic at hand :(.

One thing I don't understand is how this charge pump works. I'd expect to see two big caps, not one. So, it could worth upgrading another cap as well.

kde:

--- Quote from: exe on October 15, 2017, 09:49:45 am ---One thing I don't understand is how this charge pump works. I'd expect to see two big caps, not one. So, it could worth upgrading another cap as well.

--- End quote ---
Why two big caps? You need just one big cap to maintain the output voltage (as I understand it is connected to pin 51 and ground) and one small cap to "pump" the big one (it is connected between pins 52 and 53). Since this pump capacitor is quite small, you can charge and discharge it very quickly with relatively low current. On the other hand, if you change the pump capacitor to a bigger one, the charge current increases too and it can generate more interfernce for the ADC. So I don't think it's a good idea to increase its value. Although it could be quite harmless to increase the other (big) one.
Regarding the principle of operation itself, I think it first charges the pump capacitor to the battery voltage, then IC re-connects it so that it's voltage is added to the battery and charges the result capacitor with this doubled voltage. Then the process repeats.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod